upper surface of the cork.

If the tube has small capacity, provision should be made for catching the
overflow by inserting through the cork a small tube reaching to a
convenient height-say the 1-inch mark. The bottom of the tube projects into
a closed storage vessel. Note that the tube must be in position before the
graduation is determined, otherwise the readings will exaggerate the
rainfall.

[Illustration: FIG. 154.--Gauge in case.]

Protection against the Weather.--A rain-gauge of this kind requires
protection against frost, as the freezing of the water would burst the
tube. It will be sufficient to hinge to the front of the support a piece of
wood half an inch thicker than the diameter of the tube, grooved out so as
to fit the tube when shut round it (Fig 154).

XXVIII. WIND VANES WITH DIALS.

It is difficult to tell from a distance in which direction the arrow of a
wind vane points when the arrow lies obliquely to the spectator, or points
directly towards or away from him. In the case of a vane set up in some
position where it will be plainly visible from the house, this difficulty
is overcome by making the wind vane operate an arrow moving round a
vertical dial set square to the point of observation. Figs. 155 to 157 are
sketches and diagrams of an apparatus which does the work very
satisfactorily. The vane is attached to the upper end of a long rod,
revolving freely in brackets attached to the side of a pole. The bottom end
of the rod is pointed to engage with a nick in a bearer, in which it moves
with but little friction. Near the end is fixed a horizontal bevel-wheel,
engaging with a vertical bevel of equal size and number of teeth attached
to a short rod running through a hole in the post to an arrow on the other
side. Between arrow and post is room for a dial on which the points of the
compass are marked.

The construction of the apparatus is so simple as to call for little
comment. The tail of the vane is made of two pieces of zinc, tapering from
8 inches wide at the rear to 4 inches at the rod, to which they are clipped
by 4 screws and nuts. A stay soldered between them near the stern keeps the
broader ends a couple of inches apart, giving to the vane a wedge shape
which is more sensitive to the wind than a single flat plate. The pointer
also is cut out of sheet metal, and is attached to the tail by means of the
screws already mentioned. It must, of course, be arranged to lie in a line
bisecti